ZenovayTools

HTTP Cache Checker

Analyzes Cache-Control directives, ETag, Last-Modified, Vary, and CDN cache status headers. Explains each directive and grades caching strategy A-F.

How to Use HTTP Cache Checker

  1. 1Enter the URL to analyze caching headers.
  2. 2The tool sends a HEAD request and reads all cache-related response headers.
  3. 3Cache-Control directives are parsed and explained individually.
  4. 4Review the grade and recommendations to optimize your caching strategy.
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Frequently Asked Questions

What is Cache-Control and why does it matter?▾
Cache-Control is an HTTP header that tells browsers and CDNs how to cache a response. Without it, caches use heuristic rules — often caching for 10% of the Last-Modified age, which is unpredictable. A good Cache-Control strategy dramatically improves repeat visit performance: a 100KB page returning a 304 Not Modified (0 bytes) instead of the full response is the difference between a 200ms and a 20ms page load.
What is the difference between no-cache and no-store?▾
no-cache means 'you may cache this but must revalidate with the server before using it' — the browser stores the response and sends a conditional request (If-None-Match or If-Modified-Since). no-store means 'do not cache this at all' — no copy is kept anywhere. Use no-store for sensitive data (banking pages, health records); use no-cache for frequently-changing pages where you want the browser to revalidate.
What is stale-while-revalidate?▾
stale-while-revalidate: N allows a cache to serve a stale response while fetching a fresh one in the background. The user gets an instant response (the old version) while the next request will get the fresh version. This is ideal for pages that change occasionally — use max-age=1, stale-while-revalidate=86400 to get near-instant loads with content that updates within 1 day.
What does ETag do?▾
An ETag (Entity Tag) is a unique identifier for a specific version of a resource. When the browser has a cached response with an ETag, it sends If-None-Match: "etag-value" on the next request. If the resource hasn't changed, the server returns 304 Not Modified — saving bandwidth by not resending the full response body. ETags are more reliable than Last-Modified because they're based on content identity, not timestamps.
What is CDN cache status (CF-Cache-Status)?▾
CF-Cache-Status is a Cloudflare-specific header that shows whether the response was served from Cloudflare's edge cache. HIT = served from cache (fast, no origin request). MISS = not in cache, fetched from origin. EXPIRED = in cache but expired, refetched. BYPASS = caching bypassed (Cookie or Cache-Control: no-cache). REVALIDATED = served from cache after 304 revalidation with origin.